Wireless communication devices capable of wireless communication even when attached to a metal surface of an article include a device described in Patent Document 1 (identified below), for example.
The wireless communication device described in Patent Document 1 is formed by winding a belt-shaped metal member such as an aluminum foil around a rectangular-parallelepiped dielectric member. As a result, radiators are disposed on an upper surface and a lower surface of the dielectric member. The wireless communication device is attached to a metal surface of an article such that the radiator on the lower surface side of the dielectric member faces the metal surface of the article. Due to such a structure, even when the device is attached to the metal surface of the article, a stray capacitance between the radiator on the upper surface side and the radiator on the lower surface side of the dielectric member are substantially unchanged from before attachment to the article. Therefore, even when it is attached to a metal surface of an article, the wireless communication device can perform wireless communication in the same way as if it is not attached to the article.
Patent Document 1: Japanese Laid-Open Patent Publication No. 2012-146000.
However, it is difficult to reduce thickness in designs, such as the wireless communication device described in Patent Document 1. If the thickness of the dielectric member is reduced to make the device thinner, a distance between the radiator on the upper surface side and the radiator on the lower surface side becomes small, and the stray capacitance increases therebetween. Moreover, when the stray capacitance increases, a large amount of a current flowing through the radiator is consumed for electric field formation in the stray capacitance, and consequently, the radiation efficiency of radio waves from the radiator deteriorates. Therefore, the communication distance of the wireless communication device becomes shorter.